Artificial muscle assemblies comprising a reinforced housing

ABSTRACT

An artificial muscle includes a housing including an electrode region, an expandable fluid region, a first film layer, and a second film layer. The first film layer and the second film layer each include an inner protective layer having a first elasticity, an outer protective layer having a second elasticity, and a reinforcing layer provided between the inner protective layer and the outer protective layer, the reinforcing layer having a third elasticity greater than the first elasticity of the inner protective layer and the second elasticity of the outer protective layer. The artificial muscle further includes an electrode pair positioned in the electrode region of the housing and between the first film layer and the second film layer, and a dielectric fluid housed within the housing.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Non-Provisional patentapplication Ser. No. 17/747,416, filed May 8, 2022, for “ARTIFICIALMUSCLE ASSEMBLIES COMPRISING A REINFORCED HOUSING,” which is herebyincorporated by reference in its entirety including the drawings.

TECHNICAL FIELD

The present specification generally relates to apparatus and methods forfocused inflation on at least one surface of a device, and, morespecifically, apparatus and methods for utilizing an electrode pair todirect a fluid to inflate the device.

BACKGROUND

Current robotic technologies rely on rigid components, such asservomotors to perform tasks, often in a structured environment. Thiselasticity presents limitations in many robotic applications, caused, atleast in part, by the weight-to-power ratio of servomotors and otherrigid robotics devices. The field of soft electronic devices androbotics improves on these limitations by using artificial muscles andother soft actuators. Artificial muscles attempt to mimic theversatility, performance, and reliability of a biological muscle. Someartificial muscles rely on fluidic actuators, but fluidic actuatorsrequire a supply of pressurized gas or liquid, and fluid transport mustoccur through systems of channels and tubes, limiting the speed andefficiency of the artificial muscles. Other artificial muscles usethermally activated polymer fibers, but these are difficult to controland operate at low efficiencies. However, with repeated use the use ofthese soft electronic devices, focused inflation may result in permanentdeformation of the device and, thus, decreased performance over time.

Accordingly, a need exists for improved assemblies for reducingcomponent wear over time and maintaining initial performance standards.

SUMMARY

In one embodiment, an artificial muscle includes: a housing including anelectrode region and an expandable fluid region, the housing including afirst film layer and a second film layer, the first film layer and thesecond film layer each including: an inner protective layer having afirst elasticity; an outer protective layer having a second elasticity;and a reinforcing layer provided between the inner protective layer andthe outer protective layer, the reinforcing layer having a thirdelasticity greater than the first elasticity of the inner protectivelayer and the second elasticity of the outer protective layer; anelectrode pair positioned in the electrode region of the housing andbetween the first film layer and the second film layer; and a dielectricfluid housed within the housing.

In another embodiment, an artificial muscle assembly includes: aplurality of artificial muscle arranged in a stack, each artificialmuscle including: a housing including an electrode region and anexpandable fluid region, the housing including a first film layer and asecond film layer, the first film layer and the second film layer eachincluding: an inner protective layer having a first elasticity; an outerprotective layer having a second elasticity; a reinforcing layerprovided between the inner protective layer and the outer protectivelayer, the reinforcing layer having a third elasticity greater than thefirst elasticity of the inner protective layer and the second elasticityof the outer protective layer; an electrode pair positioned in theelectrode region of the housing and between the first film layer and thesecond film layer; and a dielectric fluid housed within the housing.

In yet another embodiment, a method for actuating an artificial muscleassembly includes: generating a voltage using a power supplyelectrically coupled to an electrode pair of an artificial muscle, theartificial muscle including: a housing including an electrode region andan expandable fluid region, the housing including a first film layer anda second film layer, the first film layer and the second film layer eachincluding: an inner protective layer having a first elasticity; an outerprotective layer having a second elasticity; and a reinforcing layerprovided between the inner protective layer and the outer protectivelayer, the reinforcing layer having a third elasticity greater than thefirst elasticity of the inner protective layer and the second elasticityof the outer protective layer; the electrode pair positioned in theelectrode region of the housing and between the first film layer and thesecond film layer; and a dielectric fluid housed within the housing; andapplying the voltage to the electrode pair of the artificial muscle,thereby actuating the electrode pair from a non-actuated state and anactuated state such that the dielectric fluid is directed into theexpandable fluid region of the housing and expands the expandable fluidregion.

These and additional features provided by the embodiments describedherein will be more fully understood in view of the following detaileddescription, in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments set forth in the drawings are illustrative and exemplaryin nature and not intended to limit the subject matter defined by theclaims. The following detailed description of the illustrativeembodiments can be understood when read in conjunction with thefollowing drawings, where like structure is indicated with likereference numerals and in which:

FIG. 1 schematically depicts an exploded view of an example artificialmuscle, according to one or more embodiments shown and described herein;

FIG. 2 schematically depicts a top view of the artificial muscle of FIG.1 , according to one or more embodiments shown and described herein;

FIG. 3 schematically depicts a top view of another example artificialmuscle, according to one or more embodiments shown and described herein;

FIG. 4 schematically depicts a partial cross-section view of a firstfilm layer of the artificial muscle of FIG. 1 taken along line 4-4 ofFIG. 1 , according to one or more embodiments shown and describedherein;

FIG. 5 schematically depicts a partial cross-section view of a secondfilm layer of the artificial muscle of FIG. 1 taken along line 5-5 ofFIG. 1 , according to one or more embodiments shown and describedherein;

FIG. 6 schematically depicts a cross-sectional view of the artificialmuscle of FIG. 1 taken along line 6-6 in FIG. 2 in a non-actuated state,according to one or more embodiments shown and described herein;

FIG. 7 schematically depicts a cross-sectional view of the artificialmuscle of FIG. 6 in an actuated state, according to one or moreembodiments shown and described herein;

FIG. 8 schematically depicts a cross-sectional view of another exampleartificial muscle in a non-actuated state, according to one or moreembodiments shown and described herein;

FIG. 9 schematically depicts a cross-sectional view of the artificialmuscle of FIG. 6 in an actuated state, according to one or moreembodiments shown and described herein;

FIG. 10 schematically depicts an artificial muscle assembly including aplurality of the artificial muscles of FIG. 1 , according to one or moreembodiments shown and described herein; and

FIG. 11 schematically depicts an actuation system for operating theartificial muscle of FIG. 1 , according to one or more embodiments shownand described herein.

DETAILED DESCRIPTION

Embodiments described herein are directed to artificial muscles andmethods of use for preventing permanent deformation of a housing of theartificial muscles resulting from repeated use. The artificial musclesgenerally include a housing including a first film layer and a secondfilm layer each including an inner protective layer having a firstelasticity, an outer protective layer having a second elasticity, and areinforcing layer provided between the inner protective layer and theouter protective layer, the reinforcing layer having a third elasticitygreater than the first elasticity of the inner protective layer and thesecond elasticity of the outer protective layer. Thus, the reinforcinglayer acts to prevent permanent deformation within the housing andparticularly within the first film layer and the second film layer.Various embodiments of the artificial muscle assemblies and theoperation of the artificial muscle assemblies are described in moredetail herein. Whenever possible, the same reference numerals will beused throughout the drawings to refer to the same or like parts.

Referring now to FIGS. 1 and 2 , an artificial muscle 100 is shown. Theartificial muscle 100 includes a housing 102, an electrode pair 104,including a first electrode 106 and a second electrode 108, fixed toopposite surfaces of the housing 102, a first electrical insulator layer110 fixed to the first electrode 106, and a second electrical insulatorlayer 112 fixed to the second electrode 108. In some embodiments, thehousing 102 is a one-piece monolithic layer including a pair of oppositeinner surfaces, such as a first inner surface 114 and a second innersurface 116, and a pair of opposite outer surfaces, such as a firstouter surface 118 and a second outer surface 120. In some embodiments,the first inner surface 114 and the second inner surface 116 of thehousing 102 are heat-sealable. In other embodiments, the housing 102 maybe a pair of individually fabricated film layers, such as a first filmlayer 122 and a second film layer 124. Thus, the first film layer 122includes the first inner surface 114 and the first outer surface 118,and the second film layer 124 includes the second inner surface 116 andthe second outer surface 120.

Throughout the ensuing description, reference may be made to the housing102 including the first film layer 122 and the second film layer 124, asopposed to the one-piece housing. It should be understood that eitherarrangement is contemplated. In some embodiments, the first film layer122 and the second film layer 124 generally include the same structureand composition. For example, as described in more detail herein, thefirst film layer 122 and the second film layer 124 each comprisesbiaxially oriented polypropylene (BOPP).

The first electrode 106 and the second electrode 108 are each positionedbetween the first film layer 122 and the second film layer 124. In someembodiments, the first electrode 106 and the second electrode 108 areeach aluminum-coated polyester such as, for example, Mylar®. Inaddition, one of the first electrode 106 and the second electrode 108 isa negatively charged electrode and the other of the first electrode 106and the second electrode 108 is a positively charged electrode. Forpurposes discussed herein, either electrode 106, 108 may be positivelycharged so long as the other electrode 106, 108 of the artificial muscle100 is negatively charged.

The first electrode 106 has a film-facing surface 126 and an oppositeinner surface 128. The first electrode 106 is positioned against thefirst film layer 122, specifically, the first inner surface 114 of thefirst film layer 122. In addition, the first electrode 106 includes afirst terminal 130 extending from the first electrode 106 past an edgeof the first film layer 122 such that the first terminal 130 can beconnected to a power supply to actuate the first electrode 106.Specifically, the first terminal 130 is coupled, either directly or inseries, to a power supply and a controller of an actuation system 400,as shown in FIG. 11 . Similarly, the second electrode 108 has afilm-facing surface 148 and an opposite inner surface 150. The secondelectrode 108 is positioned against the second film layer 124,specifically, the second inner surface 116 of the second film layer 124.The second electrode 108 includes a second terminal 152 extending fromthe second electrode 108 past an edge of the second film layer 124 suchthat the second terminal 152 can be connected to a power supply and acontroller of the actuation system 400 to actuate the second electrode108.

With respect now to the first electrode 106, the first electrode 106includes two or more fan portions 132 extending radially from a centeraxis C of the artificial muscle 100. In some embodiments, the firstelectrode 106 includes only two fan portions 132 positioned on oppositesides or ends of the first electrode 106. In some embodiments, the firstelectrode 106 includes more than two fan portions 132, such as three,four, or five fan portions 132. In embodiments in which the firstelectrode 106 includes an even number of fan portions 132, the fanportions 132 may be arranged in two or more pairs of fan portions 132.As shown in FIG. 1 , the first electrode 106 includes four fan portions132. In this embodiment, the four fan portions 132 are arranged in twopairs of fan portions 132, where the two individual fan portions 132 ofeach pair are diametrically opposed to one another.

Each fan portion 132 has a first side edge 132 a and an opposite secondside edge 132 b. Each fan portion 132 also has a first end 134 and anopposite second end 136 extending between the first side edge 132 a andthe second side edge 132 b. As shown, the first terminal 130 extendsfrom the second end 136 of one of the fan portions 132 and is integrallyformed therewith. A channel 133 is at least partially defined byopposing side edges 132 a, 132 b of adjacent fan portions 132 and, thus,extends radially toward the center axis C. The channel 133 terminates atan end 140 a of a bridge portion 140 interconnecting adjacent fanportions 132.

As shown in FIG. 1 , dividing lines D are included to depict theboundary between the fan portions 132 and the bridge portions 140. Thedividing lines D extend from the side edges 132 a, 132 b of the fanportions 132 to the first end 134 of the fan portions 132 collinear withthe side edges 132 a, 132 b. It should be understood that dividing linesD are shown in FIG. 1 for clarity and that the fan portions 132 areintegral with the bridge portions 140. The first end 134 of the fanportion 132, which extends between adjacent bridge portions 140, definesan inner length of the fan portion 132. Due to the geometry of the fanportion 132 tapering toward the center axis C between the first sideedge 132 a and the second side edge 132 b, the second end 136 of the fanportion 132 defines an outer length of the fan portion 132 that isgreater than the inner length of the fan portion 132.

Moreover, each fan portion 132 has a pair of corners 132 c defined by anintersection of the second end 136 and each of the first side edge 132 aand the second side edge 132 b of the fan portion 132. In embodiments,the corners 132 c are formed at an angle equal to or less than 90degrees. In other embodiments, the corners 132 c are formed at an acuteangle.

As shown in FIG. 1 , each fan portion 132 has a first side lengthdefined by a distance between the first end 134 of the fan portion 132and the second end 136 of the fan portion 132 along the first side edge132 a and the dividing line D that is collinear with the first side edge132 a. Each fan portion 132 also has a second side length defined by adistance between the first end 134 of the fan portion 132 and the secondend 136 of the fan portion 132 along the second side edge 132 b and thedividing line D that is collinear with the second side edge 132 b. Inembodiments, the first side length is greater than the second sidelength of the fan portion 132 such that the first electrode 106 has anellipsoid geometry.

The second end 136, the first side edge 132 a and the second side edge132 b of each fan portion 132, and the bridge portions 140interconnecting the fan portions 132 define an outer perimeter 138 ofthe first electrode 106. In embodiments, a central opening 146 is formedwithin the first electrode 106 between and encircled by the fan portions132 and the bridge portions 140, and is coaxial with the center axis C.Each fan portion 132 has a fan length extending from a perimeter 142 ofthe central opening 146 to the second end 136 of the fan portion 132.Each bridge portion 140 has a bridge length extending from a perimeter142 of the central opening 146 to the end 140 a of the bridge portion140, i.e., the channel 133. As shown, the bridge length of each of thebridge portions 140 is substantially equal to one another. Each channel133 has a channel length defined by a distance between the end 140 a ofthe bridge portion 140 and the second end 136 of the fan portion 132.Due to the bridge length of each of the bridge portions 140 beingsubstantially equal to one another and the first side length of the fanportions 132 being greater than the second side length of the fanportions 132, a first pair of opposite channels 133 has a channel lengthgreater than a channel length of a second pair of opposite channels 133.As shown, a width of the channel 133 extending between opposing sideedges 132 a, 132 b of adjacent fan portions 132 remains substantiallyconstant due to opposing side edges 132 a, 132 b being substantiallyparallel to one another.

In embodiments, the central opening 146 has a radius of 2 centimeters(cm) to 5 cm. In embodiments, the central opening 146 has a radius of 3cm to 4 cm. In embodiments, a total fan area of each of the fan portions132 is equal to or greater than twice an area of the central opening146. It should be appreciated that the ratio between the total fan areaof the fan portions 132 and the area of the central opening 146 isdirectly related to a total amount of deflection of the first film layer122 when the artificial muscle 100 is actuated, as discussed herein. Inembodiments, the bridge length is 20% to 50% of the fan length. Inembodiments, the bridge length is 30% to 40% of the fan length. Inembodiments in which the first electrode 106 does not include thecentral opening 146, the fan length and the bridge length may bemeasured from a perimeter of an imaginary circle coaxial with the centeraxis C.

Similar to the first electrode 106, the second electrode 108 includestwo or more fan portions 154 extending radially from the center axis Cof the artificial muscle 100. The second electrode 108 includessubstantially the same structure as the first electrode 106 and, thus,includes the same number of fan portions 154. Specifically, the secondelectrode 108 is illustrated as including four fan portions 154.However, it should be appreciated that the second electrode 108 mayinclude any suitable number of fan portions 154.

Each fan portion 154 of the second electrode 108 has a first side edge154 a and an opposite second side edge 154 b. Each fan portion 154 alsohas a first end 156 and an opposite second end 158 extending between thefirst side edge 154 a and the second side edge 154 b. As shown, thesecond terminal 152 extends from the second end 158 of one of the fanportions 154 and is integrally formed therewith. A channel 155 is atleast partially defined by opposing side edges 154 a, 154 b of adjacentfan portions 154 and, thus, extends radially toward the center axis C.The channel 155 terminates at an end 162 a of a bridge portion 162interconnecting adjacent fan portions 154.

As shown in FIG. 1 , additional dividing lines D are included to depictthe boundary between the fan portions 154 and the bridge portions 162.The dividing lines D extend from the side edges 154 a, 154 b of the fanportions 154 to the first end 156 of the fan portions 154 collinear withthe side edges 154 a, 154 b. It should be understood that dividing linesD are shown in FIG. 1 for clarity and that the fan portions 154 areintegral with the bridge portions 162. The first end 156 of the fanportion 154, which extends between adjacent bridge portions 162, definesan inner length of the fan portion 154. Due to the geometry of the fanportion 154 tapering toward the center axis C between the first sideedge 154 a and the second side edge 154 b, the second end 158 of the fanportion 154 defines an outer length of the fan portion 154 that isgreater than the inner length of the fan portion 154.

Moreover, each fan portion 154 has a pair of corners 154 c defined by anintersection of the second end 158 and each of the first side edge 154 aand the second side edge 154 b of the fan portion 154. In embodiments,the corners 154 c are formed at an angle equal to or less than 90degrees. In other embodiments, the corners 154 c are formed at an acuteangle. As described in more detail herein, during actuation of theartificial muscle 100, the corners 132 c of the first electrode 106 andthe corners 154 c of the second electrode 108 are configured to beattracted to one another at a lower voltage as compared to the rest ofthe first electrode 106 and the second electrode 108. Thus, actuation ofthe artificial muscle 100 initially at the corners 132 c, 154 c resultsin the outer perimeter 138 of the first electrode 106 and the outerperimeter 160 of the second electrode 108 being attracted to one anotherat a lower voltage and reducing the likelihood of air pockets or voidsforming between the first electrode 106 and the second electrode 108after actuation of the artificial muscle 100.

As shown in FIGS. 1 and 2 , in embodiments, the first side edge 154 a ofeach fan portion 154 has a first side length defined by a distancebetween the first end 156 of the fan portion 154 and the second end 158of the fan portion 154 along the first side edge 154 a and the dividingline D that is collinear with the first side edge 154 a. Each fanportion 154 also has a second side length defined by a distance betweenthe first end 156 of the fan portion 154 and the second end 158 of thefan portion 154 along the second side edge 154 b and the dividing line Dthat is collinear with the second side edge 154 b. In embodiments, thefirst side length is greater than the second side length of the fanportion 154 such that the second electrode 108 has an ellipsoid geometrycorresponding to the geometry of the first electrode 106.

The second end 158, the first side edge 154 a and the second side edge154 b of each fan portion 154, and the bridge portions 162interconnecting the fan portions 154 define an outer perimeter 160 ofthe second electrode 108. In embodiments, a central opening 168 isformed within the second electrode 108 between and encircled by the fanportions 154 and the bridge portions 162, and is coaxial with the centeraxis C. Each fan portion 154 has a fan length extending from a perimeter164 of the central opening 168 to the second end 158 of the fan portion154. Each bridge portion 162 has a bridge length extending from thecentral opening 168 to the end 162 a of the bridge portion 162, i.e.,the channel 155. As shown, the bridge length of each of the bridgeportions 162 is substantially equal to one another. Each channel 155 hasa channel length defined by a distance between the end 162 a of thebridge portion 162 and the second end of 158 the fan portion 154. Due tothe bridge length of each of the bridge portions 162 being substantiallyequal to one another and the first side length of the fan portions 154being greater than the second side length of the fan portions 154, afirst pair of opposite channels 155 has a channel length greater than achannel length of a second pair of opposite channels 155. As shown, awidth of the channel 155 extending between opposing side edges 154 a,154 b of adjacent fan portions 154 remains substantially constant due toopposing side edges 154 a, 154 b being substantially parallel to oneanother.

In embodiments, the central opening 168 has a radius of 2 cm to 5 cm. Inembodiments, the central opening 168 has a radius of 3 cm to 4 cm. Inembodiments, a total fan area of each of the fan portions 154 is equalto or greater than twice an area of the central opening 168. It shouldbe appreciated that the ratio between the total fan area of the fanportions 154 and the area of the central opening 168 is directly relatedto a total amount of deflection of the second film layer 124 when theartificial muscle 100 is actuated. In embodiments, the bridge length is20% to 50% of the fan length. In embodiments, the bridge length is 30%to 40% of the fan length. In embodiments in which the second electrode108 does not include the central opening 168, the fan length and thebridge length may be measured from a perimeter of an imaginary circlecoaxial with the center axis C.

As described herein, the first electrode 106 and the second electrode108 each have a central opening 146, 168 coaxial with the center axis C.However, it should be understood that the first electrode 106 does notneed to include the central opening 146 when the central opening 168 isprovided within the second electrode 108, as shown in the embodimentillustrated in FIGS. 8 and 9 . Alternatively, the second electrode 108does not need to include the central opening 168 when the centralopening 146 is provided within the first electrode 106.

Referring again to FIG. 1 , the first electrical insulator layer 110 andthe second electrical insulator layer 112 have a substantially ellipsoidgeometry generally corresponding to the geometry of the first electrode106 and the second electrode 108, respectively. Thus, the firstelectrical insulator layer 110 and the second electrical insulator layer112 each have fan portions 170, 172 and bridge portions 174, 176corresponding to like portions on the first electrode 106 and the secondelectrode 108. Further, the first electrical insulator layer 110 and thesecond electrical insulator layer 112 each have an outer perimeter 178,180 corresponding to the outer perimeter 138 of the first electrode 106and the outer perimeter 160 of the second electrode 108, respectively,when positioned thereon.

It should be appreciated that, in some embodiments, the first electricalinsulator layer 110 and the second electrical insulator layer 112generally include the same structure and composition. As such, in someembodiments, the first electrical insulator layer 110 and the secondelectrical insulator layer 112 each include an adhesive surface 182, 184and an opposite non-sealable surface 186, 188, respectively. Thus, insome embodiments, the first electrical insulator layer 110 and thesecond electrical insulator layer 112 are each a polymer tape adhered tothe inner surface 128 of the first electrode 106 and the inner surface150 of the second electrode 108, respectively.

Referring now to FIGS. 2, 6, and 7 , the artificial muscle 100 is shownin its assembled form. As shown in FIG. 2 , the second electrode 108 isstacked on top of the first electrode 106 and, therefore, the firstelectrode 106, the first film layer 122, and the second film layer 124are not shown. In its assembled form, the first electrode 106, thesecond electrode 108, the first electrical insulator layer 110, and thesecond electrical insulator layer 112 are sandwiched between the firstfilm layer 122 and the second film layer 124. The first film layer 122is partially sealed to the second film layer 124 at an area surroundingthe outer perimeter 138 of the first electrode 106 and the outerperimeter 160 of the second electrode 108. In some embodiments, thefirst film layer 122 is heat-sealed to the second film layer 124.Specifically, in some embodiments, the first film layer 122 is sealed tothe second film layer 124 to define a sealed portion 190 surrounding thefirst electrode 106 and the second electrode 108. The first film layer122 and the second film layer 124 may be sealed in any suitable manner,such as using an adhesive, heat sealing, vacuum sealing, or the like.

The first electrode 106, the second electrode 108, the first electricalinsulator layer 110, and the second electrical insulator layer 112provide a barrier that prevents the first film layer 122 from sealing tothe second film layer 124, thereby forming an unsealed portion 192. Theunsealed portion 192 of the housing 102 includes an electrode region194, in which the electrode pair 104 is provided, and an expandablefluid region 196, which is surrounded by the electrode region 194. Thecentral openings 146, 168 of the first electrode 106 and the secondelectrode 108 define the expandable fluid region 196 and are arranged tobe axially stacked on one another. Although not shown, the housing 102may be cut to conform to the geometry of the electrode pair 104 andreduce the size of the artificial muscle 100, namely, the size of thesealed portion 190.

A dielectric fluid 198 is provided within the unsealed portion 192 andflows freely between the first electrode 106 and the second electrode108. A “dielectric” fluid as used herein is a medium or material thattransmits electrical force without conduction and as such has lowelectrical conductivity. Some non-limiting example dielectric fluidsinclude perfluoroalkanes, transformer oils, and deionized water. Itshould be appreciated that the dielectric fluid 198 may be injected intothe unsealed portion 192 of the artificial muscle 100 using a needle orother suitable injection device.

Referring now to FIG. 3 , an alternative embodiment of an artificialmuscle 100′ is illustrated. It should be appreciated that the artificialmuscle 100′ is similar to the artificial muscle 100 described herein. Assuch, like structure is indicated with like reference numerals. Thefirst electrode 106 and the second electrode 108 of the artificialmuscle 100′ have a circular geometry as opposed to the ellipsoidgeometry of the first electrode 106 and the second electrode 108 of theartificial muscle 100 described herein. As shown in FIG. 3 , withrespect to the second electrode 108, a first side edge length of thefirst side edge 154 a is equal to a second side edge length of thesecond side edge 154 b. Accordingly, the channels 155 formed betweenopposing side edges 154 a, 154 b of the fan portions 154 each have anequal length. Although the first electrode 106 is hidden from view inFIG. 3 by the second electrode 108, it should be appreciated that thefirst electrode 106 also has a circular geometry corresponding to thegeometry of the second electrode 108.

Referring now to FIG. 4 , a partial cross-section view of the first filmlayer 122 of the housing 102 is shown. In embodiments, the first filmlayer 122 includes one or more protective layers such as an innerprotective layer 122A and an outer protective layer 122B. However, inembodiments, it should be appreciated that the first film layer 122includes only a single protective layer such as the inner protectivelayer 122A or the outer protective layer 122B. The inner protectivelayer 122A has a first elasticity and the outer protective layer 122Bhas a second elasticity. In embodiments, the first elasticity of theinner protective layer 122A is equal to the second elasticity of theouter protective layer 122B. In other embodiments, the first elasticityof the inner protective layer 122A is either greater than or less thanthe second elasticity of the outer protective layer 122B. Inembodiments, the inner protective layer 122A and the outer protectivelayer 122B each comprises BOPP, however, other suitable materials may beutilized. The inner protective layer 122A and the outer protective layer122B each has a thickness of greater than or equal to 1 mil(one-thousandth of an inch) and less than or equal to 4 mil. Inembodiments, the inner protective layer 122A and the outer protectivelayer 122B each has a thickness greater than or equal to 1 mil and lessthan or equal to 2 mil.

The first film layer 122 further includes one or more reinforcing layers122C provided between the inner protective layer 122A and the outerprotective layer 122B. The reinforcing layer 122C may be in contact witheach of the inner protective layer 122A and the outer protective layer122B and heat-sealed between and in direct contact with the innerprotective layer 122A and the outer protective layer 122B. As such, thefirst film layer 122 may include two, three, or more than fourreinforcing layers 122C provided between the inner protective layer 122Aand the outer protective layer 122B. The reinforcing layer 122C has athird elasticity greater than the first elasticity of the innerprotective layer 122A and the second elasticity of the outer protectivelayer 122B. In embodiments, the reinforcing layer 122C includescomposite a unidirectional laminate fabric material constructed from asheet of ultra-high-molecular-weight polyethylene (UHMWPE) laminatedbetween two sheets of polyester. In embodiments, the reinforcing layer122C has a thickness of greater than or equal to 1 mil and less than orequal to 4 mil. In embodiments, the reinforcing layer 122C has athickness of greater than or equal to 1 mil and less than or equal to 2mil. In embodiments, the reinforcing layer 122C is a fabric materialsuch as, for example, Dyneema®, Kevlar®, and the like. However, othersuitable materials may be utilized for the reinforcing layer 122C. Inembodiments, the first film layer 122 may include a plurality of innerprotective layers 122A and a plurality of outer protective layers 122Barranged in an alternating arrangement with one or more reinforcinglayers 122C provided between any inner protective layer 122A and anadjacent outer protective layer 122B.

Referring now to FIG. 5 , a cross-section view of the second film layer124 is shown. As discussed herein, the first film layer 122 and thesecond film layer 124 may have the same structure. As such, the secondfilm layer 124 includes one or more protective layers such as an innerprotective layer 124A and an outer protective layer 124B. However, inembodiments, it should be appreciated that the second film layer 124includes only a single protective layer such as the inner protectivelayer 124A or the outer protective layer 124B. The inner protectivelayer 124A has a first elasticity and the outer protective layer 124Bhas a second elasticity. In embodiments, the first elasticity of theinner protective layer 124A is equal to the second elasticity of theouter protective layer 124B. In other embodiments, the first elasticityof the inner protective layer 124A is either greater than or less thanthe second elasticity of the outer protective layer 124B. Inembodiments, the inner protective layer 124A and the outer protectivelayer 124B each comprises BOPP, however, other suitable materials may beutilized. The inner protective layer 124A and the outer protective layer124B each has a thickness of greater than or equal to 1 mil and lessthan or equal to 4 mil. In embodiments, the inner protective layer 124Aand the outer protective layer 124B each has a thickness of greater thanor equal to 1 mil and less than or equal to 2 mil.

The second film layer 124 further includes one or more reinforcinglayers 124C provided between the inner protective layer 124A and theouter protective layer 124B. The reinforcing layer 124C may be incontact with each of the inner protective layer 124A and the outerprotective layer 124B and heat-sealed between and in direct contact withthe inner protective layer 124A and the outer protective layer 124B. Assuch, the second film layer 124 may include two, three, or more thanfour reinforcing layers 124C provided between the inner protective layer124A and the outer protective layer 124B. The reinforcing layer 124C hasa third elasticity greater than the first elasticity of the innerprotective layer 124A and the second elasticity of the outer protectivelayer 124B. In embodiments, the reinforcing layer 124C includescomposite a unidirectional laminate fabric material constructed from asheet of UHMWPE laminated between two sheets of polyester. Inembodiments, the reinforcing layer 124C has a thickness of greater thanor equal to 1 mil and less than or equal to 4 mil. In embodiments, thereinforcing layer 124C has a thickness of greater than or equal to 1 miland less than or equal to 2 mil. In embodiments, the reinforcing layer124C is a fabric material such as, for example, Dyneema®, Kevlar®, andthe like. However, other suitable materials may be utilized for thereinforcing layer 124C. In embodiments, the second film layer 124 mayinclude a plurality of inner protective layers 124A and a plurality ofouter protective layers 124B arranged in an alternating arrangement withone or more reinforcing layers 124C provided between any innerprotective layer 124A and an adjacent outer protective layer 124B.

Referring now to FIGS. 6 and 7 , the artificial muscle 100 is actuatablebetween a non-actuated state and an actuated state. In the non-actuatedstate, as shown in FIG. 6 , the first electrode 106 and the secondelectrode 108 are partially spaced apart from one another proximate thecentral openings 146, 168 thereof and the first end 134, 156 of the fanportions 132, 154. The second end 136, 158 of the fan portions 132, 154remain in position relative to one another due to the housing 102 beingsealed at the outer perimeter 138 of the first electrode 106 and theouter perimeter 160 of the second electrode 108. In the actuated state,as shown in FIG. 7 , the first electrode 106 and the second electrode108 are brought into contact with and oriented parallel to one anotherto force the dielectric fluid 198 into the expandable fluid region 196.This causes the dielectric fluid 198 to flow through the centralopenings 146, 168 of the first electrode 106 and the second electrode108 and inflate the expandable fluid region 196.

Referring now to FIG. 6 , the artificial muscle 100 is shown in thenon-actuated state. The electrode pair 104 is provided within theelectrode region 194 of the unsealed portion 192 of the housing 102. Thecentral opening 146 of the first electrode 106 and the central opening168 of the second electrode 108 are coaxially aligned within theexpandable fluid region 196. In the non-actuated state, the firstelectrode 106 and the second electrode 108 are partially spaced apartfrom and non-parallel to one another. Due to the first film layer 122being sealed to the second film layer 124 around the electrode pair 104,the second end 136, 158 of the fan portions 132, 154 are brought intocontact with one another. Thus, dielectric fluid 198 is provided betweenthe first electrode 106 and the second electrode 108, thereby separatingthe first end 134, 156 of the fan portions 132, 154 proximate theexpandable fluid region 196. Stated another way, a distance between thefirst end 134 of the fan portion 132 of the first electrode 106 and thefirst end 156 of the fan portion 154 of the second electrode 108 isgreater than a distance between the second end 136 of the fan portion132 of the first electrode 106 and the second end 158 of the fan portion154 of the second electrode 108. This results in the electrode pair 104zippering toward the expandable fluid region 196 when actuated. Moreparticularly, zippering of the electrode pair 104 is initiated at thecorners 132 c of the first electrode 106 and the corners 154 c of thesecond electrode 108, as discussed herein. In some embodiments, thefirst electrode 106 and the second electrode 108 may be flexible. Thus,as shown in FIG. 6 , the first electrode 106 and the second electrode108 are convex such that the second ends 136, 158 of the fan portions132, 154 thereof may remain close to one another, but spaced apart fromone another proximate the central openings 146, 168. In the non-actuatedstate, the expandable fluid region 196 has a first height H1.

When actuated, as shown in FIG. 7 , the first electrode 106 and thesecond electrode 108 zipper toward one another from the second ends 136,158 of the fan portions 132, 154 thereof, thereby pushing the dielectricfluid 198 into the expandable fluid region 196. As shown, when in theactuated state, the first electrode 106 and the second electrode 108 areparallel to one another. In the actuated state, the dielectric fluid 198flows into the expandable fluid region 196 to inflate the expandablefluid region 196. As such, the first film layer 122 and the second filmlayer 124 expand in opposite directions. In the actuated state, theexpandable fluid region 196 has a second height H2, which is greaterthan the first height H1 of the expandable fluid region 196 when in thenon-actuated state. Although not shown, it should be noted that theelectrode pair 104 may be partially actuated to a position between thenon-actuated state and the actuated state. This would allow for partialinflation of the expandable fluid region 196 and adjustments whennecessary.

In order to move the first electrode 106 and the second electrode 108toward one another, a voltage is applied by a power supply. In someembodiments, a voltage of up to 10 kV may be provided from the powersupply to induce an electric field through the dielectric fluid 198. Theresulting attraction between the first electrode 106 and the secondelectrode 108 pushes the dielectric fluid 198 into the expandable fluidregion 196. Pressure from the dielectric fluid 198 within the expandablefluid region 196 causes the first film layer 122 and the firstelectrical insulator layer 110 to deform in a first axial directionalong the center axis C of the first electrode 106 and causes the secondfilm layer 124 and the second electrical insulator layer 112 to deformin an opposite second axial direction along the center axis C of thesecond electrode 108. Once the voltage being supplied to the firstelectrode 106 and the second electrode 108 is discontinued, the firstelectrode 106 and the second electrode 108 return to their initial,non-parallel position in the non-actuated state.

It should be appreciated that the present embodiments disclosed herein,specifically, the fan portions 132, 154 with the interconnecting bridgeportions 140, 162, provide a number of improvements over actuators, suchas HASEL actuators, that do not include the fan portions 132, 154.Embodiments of the artificial muscle 100 including fan portions 132, 154on each of the first electrode 106 and the second electrode 108,respectively, increases the surface area and, thus, displacement at theexpandable fluid region 196 without increasing the amount of voltagerequired as compared to known HASEL actuators including donut-shapedelectrodes having a uniform, radially-extending width. In addition, thecorners 132 c, 154 c of the fan portions 132, 154 of the artificialmuscle 100 provide zipping fronts that result in focused and directedzipping along the outer perimeters 138, 160 of the first electrode 106and the second electrode 108 during actuation as compared to HASELactuators including donut-shaped electrodes. Specifically, one pair offan portions 132, 154 provides at least twice the amount of actuatorpower per unit volume as compared to donut-shaped HASEL actuators, whiletwo pairs of fan portions 132, 154 provide at least four times theamount of actuator power per unit volume. The bridge portions 140, 162interconnecting the fan portions 132, 154 also limit buckling of the fanportions 132, 154 by maintaining the distance between the channels 133,155 and the central openings 146, 168. Because the bridge portions 140,162 are integrally formed with the fan portions 132, 154, the bridgeportions 140, 162 also prevent tearing and leakage between the fanportions 132, 154 by eliminating attachment locations that provide anincreased risk of rupturing.

In operation, when the artificial muscle 100 is actuated, expansion ofthe expandable fluid region 196 produces a force of 20Newton-millimeters (N.mm) per cubic centimeter (cm³) of actuator volumeor greater, such as 25 N.mm per cm³ or greater, 30 N.mm per cm³ orgreater, 35 N.mm per cm³ or greater, 40 N.mm per cm³ or greater, or thelike. In one example, when the artificial muscle 100 is actuated by avoltage of 9.5 kilovolts (kV), the artificial muscle 100 provides aresulting force of 20 N.

Moreover, the size of the first electrode 106 and the second electrode108 is proportional to the amount of displacement of the dielectricfluid 198. Therefore, when greater displacement within the expandablefluid region 196 is desired, the size of the electrode pair 104 isincreased relative to the size of the expandable fluid region 196. Itshould be appreciated that the size of the expandable fluid region 196is defined by the central openings 146, 168 in the first electrode 106and the second electrode 108. Thus, the degree of displacement withinthe expandable fluid region 196 may alternatively, or in addition, becontrolled by increasing or reducing the size of the central openings146, 168.

As shown in FIGS. 8 and 9 , another embodiment of an artificial muscle200 is illustrated. The artificial muscle 200 is substantially similarto the artificial muscle 100. As such, like structure is indicated withlike reference numerals. However, as shown, the first electrode 106 doesnot include a central opening, such as the central opening 146. Thus,only the second electrode 108 includes the central opening 168 formedtherein. As shown in FIG. 8 , the artificial muscle 200 is in thenon-actuated state with the first electrode 106 being planar and thesecond electrode 108 being convex relative to the first electrode 106.In the non-actuated state, the expandable fluid region 196 has a firstheight H3. In the actuated state, as shown in FIG. 9 , the expandablefluid region 196 has a second height H4, which is greater than the firstheight H3. It should be appreciated that by providing the centralopening 168 only in the second electrode 108 as opposed to both thefirst electrode 106 and the second electrode 108, the total deformationmay be formed on one side of the artificial muscle 200.

Referring now to FIG. 10 , an artificial muscle assembly 300 is shownincluding a plurality of artificial muscles, such the artificial muscle100. However, it should be appreciated that a plurality of artificialmuscles 100′ or artificial muscles 200 may similarly be arranged in astacked formation. Each artificial muscle 100 may be identical instructure and arranged in a stack such that the expandable fluid region196 of each artificial muscle 100 overlies the expandable fluid region196 of an adjacent artificial muscle 100. The terminals 130, 152 of eachartificial muscle 100 are electrically connected to one another suchthat the artificial muscles 100 may be simultaneously actuated betweenthe non-actuated state and the actuated state. By arranging theartificial muscles 100 in a stacked configuration, the total deformationof the artificial muscle assembly 300 is the sum of the deformationwithin the expandable fluid region 196 of each artificial muscle 100. Assuch, the resulting degree of deformation from the artificial muscleassembly 300 is greater than that which would be provided by theartificial muscle 100 alone.

Referring now to FIG. 11 , an actuation system 400 may be provided foroperating an artificial muscle or an artificial muscle assembly, such asthe artificial muscles 100, 100′, 200 or the artificial muscle assembly300 between the non-actuated state and the actuated state. Thus, theactuation system 400 may include a controller 402, an operating device404, a power supply 406, and a communication path 408. The variouscomponents of the actuation system 400 will now be described.

The controller 402 includes a processor 410 and a non-transitoryelectronic memory 412 to which various components are communicativelycoupled. In some embodiments, the processor 410 and the non-transitoryelectronic memory 412 and/or the other components are included within asingle device. In other embodiments, the processor 410 and thenon-transitory electronic memory 412 and/or the other components may bedistributed among multiple devices that are communicatively coupled. Thecontroller 402 includes non-transitory electronic memory 412 that storesa set of machine-readable instructions. The processor 410 executes themachine-readable instructions stored in the non-transitory electronicmemory 412. The non-transitory electronic memory 412 may comprise RAM,ROM, flash memories, hard drives, or any device capable of storingmachine-readable instructions such that the machine-readableinstructions can be accessed by the processor 410. Accordingly, theactuation system 400 described herein may be implemented in anyconventional computer programming language, as pre-programmed hardwareelements, or as a combination of hardware and software components. Thenon-transitory electronic memory 412 may be implemented as one memorymodule or a plurality of memory modules.

In some embodiments, the non-transitory electronic memory 412 includesinstructions for executing the functions of the actuation system 400.The instructions may include instructions for operating the artificialmuscles 100, 100′, 200 or the artificial muscle assembly 300 based on auser command.

The processor 410 may be any device capable of executingmachine-readable instructions. For example, the processor 410 may be anintegrated circuit, a microchip, a computer, or any other computingdevice. The non-transitory electronic memory 412 and the processor 410are coupled to the communication path 408 that provides signalinterconnectivity between various components and/or modules of theactuation system 400. Accordingly, the communication path 408 maycommunicatively couple any number of processors with one another, andallow the modules coupled to the communication path 408 to operate in adistributed computing environment. Specifically, each of the modules mayoperate as a node that may send and/or receive data. As used herein, theterm “communicatively coupled” means that coupled components are capableof exchanging data signals with one another such as, for example,electrical signals via conductive medium, electromagnetic signals viaair, optical signals via optical waveguides, and the like.

As schematically depicted in FIG. 11 , the communication path 408communicatively couples the processor 410 and the non-transitoryelectronic memory 412 of the controller 402 with a plurality of othercomponents of the actuation system 400. For example, the actuationsystem 400 depicted in FIG. 11 includes the processor 410 and thenon-transitory electronic memory 412 communicatively coupled with theoperating device 404 and the power supply 406.

The operating device 404 allows for a user to control operation of theartificial muscles 100, 100′, 200 or the artificial muscle assembly 300.In some embodiments, the operating device 404 may be a switch, toggle,button, or any combination of controls to provide user operation. As anon-limiting example, a user may actuate the artificial muscles 100,100′, 200 or the artificial muscle assembly 300 into the actuated stateby activating controls of the operating device 404 to a first position.While in the first position, the artificial muscles 100, 100′, 200 orthe artificial muscle assembly 300 will remain in the actuated state.The user may switch the artificial muscles 100, 100′, 200 or theartificial muscle assembly 300 into the non-actuated state by operatingthe controls of the operating device 404 out of the first position andinto a second position.

The operating device 404 is coupled to the communication path 408 suchthat the communication path 408 communicatively couples the operatingdevice 404 to other modules of the actuation system 400. The operatingdevice 404 may provide a user interface for receiving user instructionsas to a specific operating configuration of the artificial muscles 100,100′, 200 or the artificial muscle assembly 300. In addition, userinstructions may include instructions to operate the artificial muscles100, 100′, 200 or the artificial muscle assembly 300 only at certainconditions.

The power supply 406 (e.g., battery) provides power to the artificialmuscles 100, 100′, 200 or the artificial muscle assembly 300. In someembodiments, the power supply 406 is a rechargeable direct current powersource. It is to be understood that the power supply 406 may be a singlepower supply or battery for providing power to the artificial muscle100, 100′, 200 or the artificial muscle assembly 300. A power adapter(not shown) may be provided and electrically coupled via a wiringharness or the like for providing power to the artificial muscles 100,100′, 200 or the artificial muscle assembly 300 via the power supply406.

In some embodiments, the actuation system 400 also includes a displaydevice 414. The display device 414 is coupled to the communication path408 such that the communication path 408 communicatively couples thedisplay device 414 to other modules of the actuation system 400. Thedisplay device 414 may output a notification in response to an actuationstate of the artificial muscles 100, 100′, 200 or the artificial muscleassembly 300 or indication of a change in the actuation state of theartificial muscles 100, 100′, 200 or the artificial muscle assembly 300.Moreover, the display device 414 may be a touchscreen that, in additionto providing optical information, detects the presence and location of atactile input upon a surface of or adjacent to the display device 414.Accordingly, the display device 414 may include the operating device 404and receive mechanical input directly upon the optical output providedby the display device 414.

In some embodiments, the actuation system 400 includes network interfacehardware 416 for communicatively coupling the actuation system 400 to aportable device 418 via a network 420. The portable device 418 mayinclude, without limitation, a smartphone, a tablet, a personal mediaplayer, or any other electric device that includes wirelesscommunication functionality. It is to be appreciated that, whenprovided, the portable device 418 may serve to provide user commands tothe controller 402, instead of the operating device 404. As such, a usermay be able to control or set a program for controlling the artificialmuscles 100, 100′, 200 or the artificial muscle assembly 300 withoututilizing the controls of the operating device 404. Thus, the artificialmuscles 100, 100′, 200 or the artificial muscle assembly 300 may becontrolled remotely via the portable device 418 wirelessly communicatingwith the controller 402 via the network 420.

From the above, it is to be appreciated that defined herein areartificial muscles and methods preventing permanent deformation of ahousing of the artificial muscles resulting from repeated use. Thehousing includes a first film layer and a second film layer eachincluding an inner protective layer having a first elasticity, an outerprotective layer having a second elasticity, and a reinforcing layerprovided between the inner protective layer and the outer protectivelayer, the reinforcing layer having a third elasticity greater than thefirst elasticity of the inner protective layer and the second elasticityof the outer protective layer. Thus, the reinforcing layer preventspermanent deformation within the housing and particularly within thefirst film layer and the second film layer.

It is noted that the terms “substantially” and “about” may be utilizedherein to represent the inherent degree of uncertainty that may beattributed to any quantitative comparison, value, measurement, or otherrepresentation. These terms are also utilized herein to represent thedegree by which a quantitative representation may vary from a statedreference without resulting in a change in the basic function of thesubject matter at issue.

While particular embodiments have been illustrated and described herein,it should be understood that various other changes and modifications maybe made without departing from the scope of the claimed subject matter.Moreover, although various aspects of the claimed subject matter havebeen described herein, such aspects need not be utilized in combination.It is therefore intended that the appended claims cover all such changesand modifications that are within the scope of the claimed subjectmatter.

What is claimed is:
 1. An artificial muscle comprising: a housingcomprising an electrode region and an expandable fluid region, thehousing including a first film layer and a second film layer, the firstfilm layer comprising: an outer protective layer having an outerelasticity; and a reinforcing layer provided on an inner surface of theouter protective layer, the reinforcing layer having a reinforcingelasticity greater than the outer elasticity of the outer protectivelayer; an electrode pair positioned in the electrode region of thehousing and between the first film layer and the second film layer; anda dielectric fluid housed within the housing.
 2. The artificial muscleof claim 1, wherein the electrode pair is actuatable between anon-actuated state and an actuated state such that actuation from thenon-actuated state to the actuated state directs the dielectric fluidinto the expandable fluid region.
 3. The artificial muscle of claim 2,wherein the electrode pair comprises a first electrode positionedadjacent the first film layer of the housing and a second electrodepositioned adjacent the second film layer of the housing.
 4. Theartificial muscle of claim 3, wherein outer protective layer comprisesbiaxially oriented polypropylene.
 5. The artificial muscle of claim 4,wherein the reinforcing layer comprises a laminate fabric material. 6.The artificial muscle of claim 1, wherein the outer protective layereach has a thickness greater than or equal to 1 mil and less than orequal to 4 mil.
 7. The artificial muscle of claim 1, wherein thereinforcing layer has a thickness greater than or equal to 1 mil andless than or equal to 4 mil.
 8. The artificial muscle of claim 3,wherein: the first electrode and the second electrode each comprises twoor more fan portions and two or more bridge portions; and each of thetwo or more bridge portions interconnects adjacent fan portions.
 9. Theartificial muscle of claim 8, wherein at least one of the firstelectrode and the second electrode comprises a central openingpositioned between the two or more fan portions and encircling theexpandable fluid region.
 10. The artificial muscle of claim 1, furthercomprising a first electrical insulator layer fixed to an inner surfaceof a first electrode of the electrode pair opposite the first film layerof the housing and a second electrical insulator layer fixed to an innersurface of a second electrode of the electrode pair opposite the secondfilm layer of the housing, wherein the first electrical insulator layerand the second electrical insulator layer each includes an adhesivesurface and an opposite non-sealable surface.
 11. An artificial muscleassembly comprising: a plurality of artificial muscle arranged in astack, each artificial muscle comprising: a housing comprising anelectrode region and an expandable fluid region, the housing including afirst film layer and a second film layer, the first film layercomprising: an outer protective layer having an outer elasticity; areinforcing layer provided on an inner surface of the outer protectivelayer, the reinforcing layer having a reinforcing elasticity greaterthan the outer elasticity of the outer protective layer; an electrodepair positioned in the electrode region of the housing and between thefirst film layer and the second film layer; and a dielectric fluidhoused within the housing.
 12. The artificial muscle assembly of claim11, wherein the electrode pair is actuatable between a non-actuatedstate and an actuated state such that actuation from the non-actuatedstate to the actuated state directs the dielectric fluid into theexpandable fluid region.
 13. The artificial muscle assembly of claim 12,wherein the electrode pair comprises a first electrode positionedadjacent the first film layer of the housing and a second electrodepositioned adjacent the second film layer of the housing.
 14. Theartificial muscle assembly of claim 13, wherein the outer protectivelayer comprises biaxially oriented polypropylene.
 15. The artificialmuscle assembly of claim 14, wherein the reinforcing layer comprises alaminate fabric material.
 16. The artificial muscle assembly of claim11, wherein: the outer protective layer each has a thickness greaterthan or equal to 1 mil and less than or equal to 4 mil; and thereinforcing layer has a thickness greater than or equal to 1 mil andless than or equal to 4 mil.
 17. The artificial muscle assembly of claim11, wherein: the electrode pair includes a first electrode and a secondelectrode, the first electrode and the second electrode each comprisestwo fan portions and a bridge portion; the bridge portion interconnectsadjacent fan portions; and at least one of the first electrode and thesecond electrode comprises a central opening positioned between the twofan portions and encircling the expandable fluid region.
 18. A methodfor actuating an artificial muscle assembly, the method comprising:generating a voltage using a power supply electrically coupled to anelectrode pair of an artificial muscle, the artificial musclecomprising: a housing comprising an electrode region and an expandablefluid region, the housing including a first film layer and a second filmlayer, the first film layer comprising: an outer protective layer havingan outer elasticity; and a reinforcing layer provided on an innersurface of the outer protective layer, the reinforcing layer having areinforcing elasticity greater than the outer elasticity of the outerprotective layer; the electrode pair positioned in the electrode regionof the housing and between the first film layer and the second filmlayer; and a dielectric fluid housed within the housing; and applyingthe voltage to the electrode pair of the artificial muscle, therebyactuating the electrode pair from a non-actuated state and an actuatedstate such that the dielectric fluid is directed into the expandablefluid region of the housing and expands the expandable fluid region. 19.The method of claim 18, wherein: the outer protective layer comprisesbiaxially oriented polypropylene; and the reinforcing layer comprises alaminate fabric material.
 20. The method of claim 19, wherein: the outerprotective layer each has a thickness greater than or equal to 1 mil andless than or equal to 4 mil; and the reinforcing layer has a thicknessgreater than or equal to 1 mil and less than or equal to 4 mil.